An alternative is to replace a surface-mount component on the main circuit board with a different value to accommodate the dimming LED in the sensor. This modification was posted in I think 2011 by a USA uni prof - I forget who. The left bump sensor relevant component to be replaced is R87, a 20k resistor (marked 203 in sm value coding). For the right bump sensor it is R82 again a 20k resistor of course. In each case the component to be removed and replaced is sited adjacent and parallel to a 1k resistor (sm marking 102), R86 and R83 respectively. He suggested using 130k resistors as replacement components, I used 220k to get a few more years out of my ageing Roomba 530. 1/8th watt conventional resistors fit reasonably well in place of the sm devices. It seems the section of the main circuit board containing the parts to be replaced is common to many of the model numbers, including component IDs and layout even when other parts of the board differ to the extent of including extra switches for some models.